Torsional Vibration calculation for hull and machinery to be carried out by Builder and engine manufacturer to summarise the reciprocal of hull, machinery and propeller. Further the comments of the Classification Society on the vibration characteristics must be forwarded to Owner.
During structural design proper care to be taken to ensure adequate scantlings, continuity and support to allow for occurring dynamic effects.
Vibration measurements to be carried out on vessel’s hull, accommodation, engine room, azimuth thruster and local elements during sea trials with the main engine developing up to 100% MCR as well as bollard pull condition. If the result for the first vessel is found satisfactory by owner, the vibration measurement shall not be carried out for subsequent vessels.
Vibrations occurring in hull and superstructure in crew accommodation and working spaces normally attended by watching crew to be judged according to ISO 6854-
1984 “Mechanical vibration and shock – Guidelines for the overall evaluation in merchant ships”. See sketch 1.
The design target shall be based on the lower boundary of the hatched zone.
Generally measured root mean square (RMS) of total vibration spectrogram 1 – 100 Hz to be lower than 5.6 mm/sec. RMS.
If measured RMS values exceed 5.6 mm/s RMS, narrow band vibration measurements to be judged according to sketch 1.
If measured values exceed the upper boundary line of the hatched zone with the vessel in normal operating condition up to 90% MCR, corrective actions to be taken through mutual discussions between Owner and Builder.